Plc help

[clotworthy]

what are the advantages of using PLCs as opposed to traditional relay logic systems.

 

[GregPLC]

I wish I had enough energy left in me today to come up with a humorous comment...Perhaps if you read a couple pages further in your book, you will get the answer you are looking for...I do give you credit, you did bother to register.

Greg

 

[Allen Nelson]

No free rides. Sorry.

I don't mean to give a flip answer to a hard-working HNC student, but what do you think?

Seriously, what do you think the reasons are. If you tell us what you think, we'll tell you if you're right.

 

[clotworthy]

they're smaller and quieter, is it as simple as that? I'm just looking for some sound reassurance, hope you can help

 

[GregPLC]

Well, depends....though I'm not sure that is a key answer a teacher would be looking for.

 

[Allen Nelson]

Smaller is one, but not very important answer. When you build a factory the size of a football field, whether your control system is in a closet-sized box or one the size of a room, isn't going to be very important.

As for noise, that's even less important. Not many people are going to around the control system once it's operating.

I'll give you a hint:

£

(or $ for us in the US; € on the continent).

Now can you tell me why?

 

[Ron Beaufort]

and what about making changes to the machine's sequence of operations ... which system do you think would be the easier one to modify? ...

 

[akreel]

How do you think you could do data logging in a relay system?

Could you think of a way to make a relay panel display real-time analog readings, like pressures or flows? It sure would be fun to try!

 

[clotworthy]

Are there any good web sites i can visit to learn more about PLC's

 

[Ron Beaufort]

I fear to watch ... yet I cannot look away ...

ok ... now you're really asking for it ...

------------

edit: seriously ... welcome to the forum ...

 

[PLucas]

Clotworthy

Allen and Ron have both given you answers that should point you in the right direction, cost, ease of modification. Have a think about the components used within a 'relay logic' controller and a PLC, what one would be easier to maintain? That would also involve cost.

What one would also look nicer?

A nice neat little blue or black box with some pretty flashing lights or a load of relays with no flashing lights??

Now then, do I detect a 'mellowing out' from our more 'senior' members towards the dreaded HNC students?? Or is it the case that he didn't ask THAT question? You know the one!

edit

I see that while I was typeing, some other replies were posted, perhaps I don't detect a mellowing out towards HNC students

Paul

P.S Clotworthy, you will not find a better web site anywhere in the known universe to learn PLC's.

 

[Allen Nelson]

Soft?

Mellowing out? No way!

If he were to try to say that a PLC system costs less, I am quite prepared to ream him over the coals for stupidity.

After all, how can a $5000 PLC be cheaper than some $2 relays?

And yet, PLCs are justified to corporate executives based on cost. So how can that be? (Fie on Ron and Aaron for giving too big of hints).

 

[Ron Beaufort]

from Allen:

Fie on Ron for giving too big of hint

sorry, Allen ... I was typing mine and didn't notice yours before I posted ... and yes, I'll admit ... I WAS feeling a little bit mellow today ... I was trying to think up a way to give a vague hint ... I'll try to remember your £ and $ signs next time ...

or will there actually BE a next time? ... yeah, I'm pretty sure there will be ...

 

[PLucas]

Re: Soft?

After all, how can a $5000 PLC be cheaper than some $2 relays?

And yet, PLCs are justified to corporate executives based on cost. So how can that be?

Allen,

I assume that your questions are aimed at clotworthy to get him to think about the answer to his original question, or are they up for anyone to answer?

A while ago I removed relays and such like from a troublesome bit of kit, fitted it with a nice new PLC with a HMI that cost £6000, the parts I removed and threw in the bin (trash to you guys) probably cost no more than £500, so where is the sense in that? I know that by doing what I did, the PLC and HMI have paid for themselves and saved my company more money, so the question for clotworthy is, how can this be?

Answer that and you will have another advantage of a PLC over relay logic.

Paul

 

[GregPLC]

Of course you don't need software and a propriatary interface cable for relays ;-) Perhaps they are more economical.